<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .one {
      width: 100px;
      height: 100px;
      border: 1px solid black;
      border-radius: 50px  0px  50px 50px;
    }
    .two {
      width: 100px;
      height: 100px;
      border: 50px solid black;
      border-left-width: 0px;
      border-bottom-width: 0px;
      border-radius: 100px;
    }
  </style>
</head>
<body>
   <!-- border-radius 小技巧 width == height, 正方形
     1 画出各种小灯泡， 一个角设置为0 ，其余角设置为宽度的一半
     2 半月形，需要选择相领的2对边进行圆角，其它边的宽度设置为0s
    -->
   <div class="one"></div>
   <div class="two"></div>
</body>
</html>